1. Field of the Invention
The present invention generally relates to a method of objectively calculating a priority for repair of cable leakage interference to Long Term Evolution (LTE) cellular service. More specifically, parameters and metrics are identified, as incorporated in a software-implemented tool, to permit cable operators to establish priorities for repair of cable leaks in their system.
2. Description of the Related Art
The Federal Communication Commission (FCC) protects the use of over-the-air frequencies based on their allocation of use. Anyone or anything that causes unauthorized interference on over-the-air frequencies is subject to the rules and regulations set by FCC. One such protected air space is the FAA band used for aircraft communications which is generally located between 108 MHz and 137 MHz. This same frequency band is used by cable operators for cable TV services.
However, their signaling is distributed through hardline cable infrastructure. In order to prevent interference caused by the cable TV signals in the over-the-air FAA band, cable operators must ensure that their cable infrastructure does not allow the cable signals to escape into the air, often referred to as “cable leakage.” If the shielding integrity of their cable infrastructure is compromised in such a manner that cable leakage escapes into the FAA band, the cable operators are required to repair their infrastructure to eliminate these leaks.
In order to ensure that cable operators are in compliance with non-interference in the FAA band, the FCC has mandated that cable operators will report that at least 75% of their cable plant every year has been checked, record any leaks found, and fix the leaks to a point where the Cumulative Leakage Index (CLI) is below the threshold set by the FCC. Operators must also monitor their leakage by substantially covering their plant every three months. Records must be kept on file validating that the cable operators have checked their cable plant four times each year and they must keep records of all leaks found greater than 20 uV/m at 3 meters.
With the emergence of the new 4G Cellular service or Long Term Evolution (LTE) located in the 700 MHz to 800 MHz frequency domain and potentially 600 MHz to 700 MHz in the future, there are early reports and studies that show cable leakage in this frequency band is interfering with the LTE service. The LTE signaling, by its nature, is more sensitive to certain types of interference than the previous cellular technologies such as Edge and 3G. While the FCC has not yet created specific regulations for the cable operators to monitor and report such interference, the standing rule still applies that no unauthorized interference can exist in over-the-air services.
This creates several technical problems for cable operators as more and more LTE equipment is deployed:
1) The majority of cable channels in the LTE band are modulated using digital QAM (Quadrature Amplitude Modulation) versus analog carriers, which in turn produces “digital leakage” when there are integrity flaws in the cable plant. The current cable leakage detection equipment deployed by cable operators is analog-based, which means their existing equipment cannot detect the digital leakage. Cable operators will need new equipment that is capable of detecting digital leakage;
2) Unlike the FAA band, LTE signaling has a vast distribution network consisting of cellular towers and handheld cell phones. This means that the power level of the LTE signal will vary greatly depending on the distance from the cell towers and terrestrial obstructions such as buildings, tunnels, mountains, etc. The LTE signal quality from either the cellular tower and/or the handheld device will affect the amount of interference that a cable leak will have on the LTE signal, making it difficult to determine which leaks are causing the most damaging interference;
3) The digital leaks also vary in power level, which adds another variable further complicating the ability to determine the impact severity a leak is causing on the LTE signaling. Generally, the higher the power level of the leak, the more potential it has of causing harmful interference. In order to meet the FCC CLI guidelines, cable operators typically prioritize which leaks to fix based on the leak power level—the higher the leak power level, the higher the priority to repair the leak. However, the ability to prioritize leaks that are causing harmful LTE interference is now much more complex than merely using the leak power level on its own.
For example, a small leak which was conventionally considered to be low impacting in the FAA domain may now be a much bigger problem from an LTE perspective. If a small cable leak exists where the LTE service has poor performance, it may cause enough interference to further deteriorate the LTE service below an acceptable operating point.
In summary, cable operators will need to find and fix cable leakage that is causing harmful interference in the LTE band. They will need both new products and tools to help them detect and characterize the severity of the interference so they can prioritize their resources to fix these leaks accordingly.